Silicon wafers are widely used as substrates on which multilevel integrated circuits are fabricated. Integrated circuits on a semiconductor wafer are typically manufactured with insulating layers, semiconductive layers, such as polysilicon, and conductive metals substrate layers, such as tungsten, aluminum, copper and platinum. The dielectric materials can be a dielectric, such as, silica including thermally grown SiO2 and chemical vapor deposited SiO2 using tetraethylorthosilane gas (TEOS). Further, advanced integrated circuits often employ low K dielectric materials.
In circuit fabrication, a series of deposition and etch steps is required to form a multi-level pattern on semiconductor wafer. A non-planar surface is created during these manufacturing processes, which can cause focusing problems for photolithography equipment. Poor focusing during lithographic alignment and registration results in low yield and decreased device performance.
A polishing method known as chemical-mechanical-polishing or planarization (CMP) is often used to polish a non-planar wafer during circuit fabrication. CMP processes can be used to planarize insulating layers, such as dielectric material, conductive metals and semiconductive layers by utilizing different polishing slurry and polish pad configurations. For example, CMP processes are used in multi-layer interconnection structures having overlying aluminum alloy layers to flatten the interlayer dielectric films. Also, CMP is required to form tungsten plugs and inlayed of interconnection structures. For higher speed integrated circuits, copper lines with low resistance are used in damascene structures. Due to the difficulty and high cost associated with dry etching copper alloys, trenches or damascene structures are dry etched into dielectric films and then filled with barrier layer followed by copper seed and electroplating of copper. Copper CMP is use to remove excess material above the inlaid trench.
Slurries used in copper CMP typically include an abrasive, an oxidizing agent, a complexing agent or ligand, a corrosion inhibitor, such as benzotriazole (BTA) and other compounds that act as protective film or act as surfactant. For slurries with a high concentration of BTA, a copper-BTA compound (Cu-BTA) is formed as chemical reaction by-product. Both abrasive-free and reactive liquid slurries used in copper CMP can generate insoluble residues during polishing, such as Cu-BTA complex compounds and other BTA-Cu-organic polymer complexes. At high copper removal rates or high copper dissolution rate, the copper ion concentration exceeds maximum solubility (Ksp). With a high concentration of available BTA, Cu(I)-BTA compounds precipitate from solution, and at high concentration, coagulate into a surface residue having the consistency of chewing gum. When a high concentration of polymer ligand is available, a Cu(II)-polymer complex can precipitate and coagulate with Cu-BTA to form an amorphous mixture or chain-terminated structure.
During polishing, the insoluble Cu-BTA residues stick to the surface of the pad and accumulate to the point of eventually filling the grooves in the polish pad. The accumulation of insoluble residue in the pad grooves and micro-pores disturbs the normal slurry flow pattern. Since the slurry flow pattern is especially disturbed in areas where the wafer contacts the polish pad, the residue adversely affects polishing uniformity. Also, the copper removal rate decreases as the residue builds up during polishing.
To combat the deleterious effects of the insoluble residues, manufacturers have attempted to mechanically remove the residues from the wafer surface by frictional contact with a polishing pad. As the residue film is removed, however, just as during copper polishing, the copper complex accumulates on the polishing pad and fills grooves in the pad surface. De-ionized water (DI-water) is normally used during pad conditioning to help lubricate the pad and to remove debris from the pad. A high-pressure DI-water spray is used to speed up the cleaning process in CMP machines equipped with a pressure sprayer. Due to insolubility of slurry by-products, however, DI-water is largely ineffective at cleaning the pads and even a high pressure DI water spray is ineffective in removing the sticky BTA-Cu-polymer complex.
Although, conventional diamond grid disks are widely used to remove debris from polishing pads, the disks only condition the surface of the pad and cannot remove the residue within the polish pad grooves. Also, brush conditioners simply disturb the residue within the grooves and are largely unable to condition the pad surface and remove the residue. Using conventional cleaners in combination with a condition brush can be effective at reducing the residue on the polishing pad, but this process requires long condition times, which reduces the overall throughput of the polisher. Also, due to the slow dissolution kinetics of Cu-BTA complex residue in conventional cleaners, the condition brushes become contaminated during the conditioning process. Further, even in-situ conditioning during polishing with a diamond conditioner disk does not efficiently remove the insoluble residues within the pad groove. Accordingly, a need existed for a cleaning solution that can effectively remove complex insoluble copper residues from wafer and polishing pad surfaces.